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Dependable by design

Paul E Eden takes a closer look at new Pratt & Whitney engine innovations from turboprop to narrowbody jet platforms
 

Pratt & Whitney’s rapidly maturing PW1000G geared turbofan has had teething problems to overcome, but nonetheless delivered the promised fuel savings and reduced emissions out of the box. Meanwhile, Pratt & Whitney Canada’s turboprops are continuing their domination of the regional propliner market.

 

There had been geared turbofan designs before. Garrett’s TFE731, latterly a Honeywell product, has been successfully powering business jets and a variety of military aircraft since the early 1970s. Through another series of acquisitions, Honeywell also became the most recent producer of Lycoming’s ALF502 and derived LF507, primarily equipping the BAE 146 and Avro RJ regional airliners, respectively.

 

But with its PW1000G Geared Turbofan (GTF), Pratt & Whitney (P&W) took the concept further, producing an engine magnitude more powerful than either the TFE731 or LF507, aimed at a new generation of regional jets and short/medium haul airliners designed for dramatically reduced fuel burn and emissions. The BAE 146 pioneered jet operations at London City thanks to the exemplary field characteristics of the 146-100 and the low noise signature of its geared engines; both the 146 and RJ still make good, quiet neighbours at busy regional airports and P&W set out to reduce the inherently low noise of a geared turbofan even further.

 

Meanwhile, Pratt & Whitney Canada (P&WC) has maintained its dominance of the regional turboprop market, PW100-series engines driving all ATR models and every derivative of the Dash 8, latterly developed by Bombardier into the high-performance Q400 – and now once again under the de Havilland Canada brand – after Longview Aviation Capital purchased the programme. Longview also owns Viking Air, offering support to the legacy DHC-6 Twin Otter fleet and the modernised, new production Twin Otter Series 400, continuing a line founded on P&WC PT6A power in the 1960s and which has remained faithful to the engine ever since.

 

GTF revolution

Variants of the PW1000G are offered for the Airbus A320neo Family, Airbus A220 (formerly Bombardier CSeries), Embraer E2, Irkut MC-21 and Mitsubishi SpaceJet. After extensive ground and air testing, the GTF powered a production airframe in flight for the first time during September 2013, when the CSeries completed its maiden sortie on PW1500G power. One year later, the A320neo followed, rapidly entering the PW1100G into widespread service from January 2016.

 

Compared to contemporary CFM56 and V2500 powerplants, PW1100G fuel consumption was immediately improved – perhaps by as much as 17 or 18% – but there were also problems. Various issues with thermal conditions affecting materials at different rates, seals and vibration caused extended engine start times and a number of early engine removals for repair. Pratt & Whitney’s extensive rectification efforts are continuing to pay dividends, even as cycle limits were amended for the high-pressure compressor hub of the A220’s PW1500G and the PW1900G powering the E2, following the discovery of corrosion.

 

Today’s in-service GTF boasts an almost perfect dispatch rate thanks in no small part to P&W’s proactive work. Looking back on its problems, company spokeswoman Jenny Dervin says: “As the first clean-sheet propulsion design for commercial aviation in almost 30 years, we expected some entry into service issues. Our digital design and testing tools are world class, but there are issues you only find once you put some hours on the engine. We’re pleased the Geared Turbofan performed as promised out of the gate, with 16% better fuel efficiency, 50% lower emissions and a 75% smaller noise footprint.

 

“The early issues dealt mostly with seals and life-limited parts that required replacement. As we ramped up production, we also ramped up our aftermarket network in order to take care of the fleet. We have more than 10,000 Geared Turbofan orders and our aftermarket network is growing to support that fleet.”

 

Pratt & Whitney customers already enjoyed access to a global support network, but the GTF introduced new technologies, new parts requirements and a number of first time P&W customers. It also entered service in quite different variants, ranging in thrust from around 35,000lb (160kN) for the most powerful PW1100G down to 15,000lb (67kN) for the SpaceJet’s PW1200G; incidentally, P&W applies PurePower branding to the GTF technology and the P&WC PurePower PW800 engines powering the Gulfstream G500 and G600, and chosen for the forthcoming Dassault Falcon 6X, are based on PW1000G cores.

 

Supporting this ambitious array of engine variants and technologies might have presented a headache, but Dervin notes: “The five variants of GTF don’t drive complexity from an engineering or production standpoint. The GTF architecture is a shared concept among all variants, extending to the PW800 core.” There are currently seven active GTF MRO engine shops: Pratt & Whitney Columbus Engine Center [CEC] in Georgia and Pratt & Whitney West Palm Beach in Florida, US; Lufthansa Technik [LHT] in Hamburg and Alzey, and MTU Aero Engines in Hannover, Germany; IHI Aerospace in Mizuho, Japan; and Pratt & Whitney Eagle Services Asia [ESA] in Singapore. By 2020, there will be ten active GTF MRO centres. She also explains that of more than 10,000 engines ordered, the majority are for the A320neo Family and thus: “…parts provisioning for MRO will not be appreciably complex or revenue-draining.”

 

Ignoring unscheduled visits, a modern turbofan typically comes off-wing every six years for major servicing and maintenance. No GTF has yet fallen due for overhaul therefore, but when it does, Dervin expects P&W’s service network to be well prepared. “We learned a great deal about the engine as we ramped up the aftermarket network, including the vital hands-on experience of our technicians, so we feel comfortable meeting the future challenge of servicing the engine at scale.”

 

Meanwhile, GTF production is still ramping up and orders continue to accrue – how are the spare engine pool and parts supply chain holding up? “We’ve actually seen a significant reduction in required spares to support operations since last year, and today our spare pool is closer to standard industry ratios. The spare pool ratio to the flying fleet will remain consistent as the fleet grows,” Dervin confirms. What’s more, P&W will be better informed than ever on how the engine is maturing. “The GTF family engines have 40% more sensors, so the operating fleet is providing a wealth of information regarding performance and maintenance prognostics.”

 

FAST solution

Pratt & Whitney fully exploits aircraft connectivity in its support efforts for regional and business aviation customers, downloading engine data that not only monitors performance, but also provides early warning of developing problems. Telling a customer in advance of an emerging issue can help them incorporate the fix at their next scheduled maintenance event or help source replacement parts at their MRO of choice, potentially avoiding a more costly and inconvenient AOG. Similar technology is available on the PW1500G.

 

“Our eFAST and FAST [Full-flight data Acquisition, Storage and Transmission] solution ecosystem allows us and our operators access to full-flight engine data, which is transmitted by cellular or Wi-Fi connection once the plane lands. Offered under our expanding suite of digital engine services, FAST enhances engine and aircraft ‘connectivity’ through its ability to provide situational awareness about engine health, usage and trends. FAST is available across several aircraft applications in business and general aviation, and on regional types powered by the PW100 and PW150 series turboprops. eFAST capability is also built into GTF engines built for the Airbus A220 and has received a supplemental type certificate [STC] for the V2500-powered Airbus A321.”

 

Dervin’s mention of the V2500 is an important reminder that P&W continues to support thousands of examples of the IAE product, as well as the PW6000 engines powering a relatively small number of A318s. She confirms: “We are committed to maintaining our customers’ fleets for as long as they operate the engine. And, on more mature programmes, Pratt & Whitney’s global network of aftermarket facilities offers a choice of service providers.”

 

Turboprops

While the GTF emerged from a clean sheet, P&WC’s current PW100 and derived PW150 turboprops are the latest evolutions of an engine line that entered service in the early to mid-1980s. Dervin says: “Every engine programme, no matter the manufacturer, is in a constant state of improvement. There are always new ways to enhance performance or extend engine life and Pratt & Whitney has continually invested in new PW100/150 technologies.

 

Dervin continues saying today’s engines consistently set every benchmark when it comes to fuel burn, CO2 emissions and dispatch reliability. “The use of software, especially in electronic engine controls, is also far more prevalent today than when the first engines were launched. This makes for ‘smarter’ engines that allow us to offer digital diagnostic and prognostic solutions, including FAST, which move operators away from unplanned maintenance events to planned maintenance, increase dispatch availability and heighten reliability.

 

“Our investment also results in new customer service products and solutions to optimise performance, reduce maintenance costs and help ensure adherence to flight schedules. For example, oil analysis technology facilitates health monitoring of oil-wetted parts, including carbon seals, enabling early detection – up to hundreds of hours in advance – of a potential issue.”

 

Older still in original design, the rugged PT6A continues to set reliability standards. With almost 50,000 engines produced in 72 certified models, the PT6A remains a stalwart at the smaller end of regional operations, it has also been selected – in thoroughly modern PT6A-65SC form – for Cessna’s forthcoming SkyCourier twin-engined utility aircraft. According to Dervin, the -65SC is: “Engineered for high payloads and sets a new benchmark offering proven dispatch reliability and crucial high-power take-off and climb. Its advanced technologies include FAST. The PT6A-65SC also offers more time on-wing, with a class-leading 6,000-hour time between overhaul.”

 

Future propulsion

The ATR -600 models, and de Havilland Canada Q400 deliver efficient, reliable service in the regional market, but the need for an all new turboprop is becoming increasingly apparent. A ready market is likely to open up as options for replacement of either or both types are realised, and a modern turboprop will likely be even more efficient, and barely slower, than a regional jet on shorter routes. Indeed, Dervin notes that PW100-powered turboprops consume 25% to 40% less fuel and produce 50% lower CO2 emissions than similar-sized regional jets.

 

There are rumblings at ATR and Embraer over the possibilities for future turboprop transports and P&WC is likely to want to maintain its dominance with a new engine. Confirming that ‘mission needs determine the engine solution’, Dervin suggests the airframe OEMs are best placed to comment on future products.

 

Which leaves the GTF, establishing itself in service and hopefully with the majority of its teething problems behind it. Pushing those headline-grabbing issues aside, P&W actually managed to produce an engine that delivered everything it said it would, through the incorporation of advanced technologies and complex engineering in an all new design. Significantly, Dervin proudly explains: “The GTF engines operating today are the first generation of this new architecture. The family has a very long runway for growth.”


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